The following discussion is extracted from "DIFFUSION CHAMBER METHOD FOR IN SITU MEASUREMENT OF PATHOGEN INACTIVATION IN GROUNDWATER", Paul Pavelic, et. al, Water Resources 32(4), pg. 1144 (1998):
"An understanding of the survival of pathogenic organisms (through the use of indicator or enteric species) is used to minimize the risk of infection. Clearly, the longer a pathogen survives in the environment, the greater the probability of transmitting infection. Transmission of infection by pathogens present in abstracted groundwaters was one of the earliest recognized public health problems--that of cholera, discovered by John Snow at the Broad St. pump in London. PA1 "The subsurface environment is one which tends not to favor the survival of introduced microorganisms. Survival (and transport) of pathogenic microorganisms depends on the nature of the porous media, environmental conditions, and the type of microorganism. . . . A number of techniques have been used to measure pathogen inactivation in groundwater, although each of these have particular advantages and disadvantages. Laboratory batch experiments are simple and the most commonly used. However the extent to which these replicate the subsurface conditions is questionable, because of, for example, the lower hydrostatic pressure and redox effects (exposure to O.sub.2) that are associated with their use in the laboratory. That is, processes governing survival may differ between the laboratory and the field. Therefore, availability of techniques to measure rates of pathogen inactivation in situ is an attractive development. PA1 "Field isolation methods, where organisms are introduced directly into the groundwater, have been attempted, but can be extremely difficult to interpret due to mixing between introduced and ambient waters within the aquifer, the differential residence times of abstracted waters, and the impact of indigenous organisms. There are also public health considerations in relation to uncontrolled release of pathogens into the environment. PA1 "The containment of well-defined suspensions of microorganisms within dialysis tubing is a relatively simple and inexpensive approach to determine in situ inactivation rates. However dialysis tubing is composed of cellulose, which can be catabolised by bacteria, making it fragile and so subject to tearing. Hence it may not be a reliable experimental technique to use under field conditions. PA1 "Use of diffusion chambers for studying microbial survival was first reported by McFeters and Stuart, (1972), and applied to studies of natural surface waters. Diffusion chambers are similar to dialysis tubing, but have the advantage of using an inert polycarbonate membrane, which allows diffusive flow across the chamber membrane. Other workers who have reported use of diffusion chambers in groundwater studies are: McFeters et al. (1974) for indicator bacteria and Keswick et al. (1982) for enteric viruses and indicator bacteria. In both cases, the chambers were placed in tanks where groundwater flowed past them while being pumped continuously from a well. The high flow of water past the chambers was not representative of groundwater conditions, whilst the tank overflow provides a large artifact. PA1 "Since each chamber required individual housing, there was considerable effort and much replication, in chamber construction and preparation. And since the dimensions were also reduced to fit in small diameter wells, the Plexiglas bodies of the chambers became fragile, and thus susceptible to damage. . . . Several means of sterilizing the plexiglass chambers were tested or explored, autoclaving, chemical disinfection, microwave and radiation, and difficulty was found with each. For instance, attempts to autoclave the Plexiglas chambers resulted in their deformation, which also made them prone to leakage."
Pavelic proposed a diffusion chamber consisting of a frame and detachable matching side-pieces that are constructed from nylon. Holes were bored into this frame. and two filter membranes attached by side-pieces to create the surface area of the chamber. Polycarbonate membrane filters of 0.025 um pore-size (Millipore Type VS) with nylon mesh reinforcing on the outer surface are trimmed to size and sandwiched firmly between the side pieces and main frame by stainless steel screws. Two holes were drilled into one side of the chamber to allow catheter single lumen PVC tubing (0.59 mm ID) for injecting sampling and re-injecting the fluid from the chamber using a syringe. Excess catheter tubing was fed into a hole drilled into the frame. Liquid flowing silicon glue also provided watertight seals along all joints. The Pavelic chambers were thus expensive, time-consuming and complicated to build and use--"we anticipate that seven person-hours of work, spread over two days, is required per assembly" (of nine chambers).
Kennedy, U.S. Pat. No. 3,787,183, "METHOD OF ANALYZING CATALYST ACTION", presents a method of analyzing a catalyst by burying samples of a catalyst in durable perforate containers at known locations in a larger body of catalyst. No use of sentinel organisms is shown, and the method is intended to study the catalyst itself, not the effect of the catalyst (environment) on organisms. The perforate containers are of different structure from the sentinel chambers of the invention.
Michaels, et al, U.S. Pat. No. 4,440,853, "MICROBIOLOGICAL METHODS USING HOLLOW FIBER MEMBRANE REACTOR", teaches the use of microorganisms for processing organic material, where the organisms are suspended in a spongelike structure surrounding a semipermeable membrane.
Cullimore, et al, U.S. Pat. No. 5,187,072, "METHOD AND APPARATUS FOR THE DETERMINATION OF FERMENTATIVE ANALYTIC CULTURED ACTIVITIES", uses an inverted test chamber in a medium to study an organism. The production of gas by the organism causes the chamber to float.
Nolte, et al, U.S. Pat. No. 5,307,694, "SAMPLE HOLDER FOR HYDROUS PYROLYSIS OPERATIONS", shows the use of a similar sample chamber to the invention, in that the sample chamber comprises a cylindrical tube with filters at each end, within which a sample is placed. However, no medium or sentinel microorganism is used, and the use of the chamber is quite different, involving solvents and vacuum analysis and high temperatures to extract hydrocarbons.
Machelsky, et al, U.S. Pat. No. 5,516,648, "ENCAPSULATED BIOLOGICAL INDICATOR", encapsulates reference microorganisms in an interior cavity of a microporous membrane, rather than a sentinel chamber.
Hollingshead, U.S. Pat. No. 5,698,413, "METHOD OF EVALUATING CHEMOTHERAPEUTIC AGENTS IN VIVO", implants semipermeable encapsulation devices containing target cell lines into laboratory animals for studying the effect of chemotherapy on the cell lines.